1. Field of the Invention
This invention relates to a device for rotating a water-wheel in the air by an electric motor while the water-wheel is in spinning reserve.
2. Description of the Prior Art
A water-wheel may be placed in spinning reserve besides being operated for producing electric power or performing a pumping operation. When a water-wheel is placed in spinning reserve, compressed air is introduced into the runner chamber of the water-wheel to move downwardly the liquid level of water in the runner chamber and the runner is rotated in the compressed air by a generator-motor. A water-wheel is placed in spinning reserve to attain several ends. For example, it will be placed in spinning reserve for purposes of reducing the starting torque of the generator-motor when a pumping operation is begun or letting it stand by to be ready for switching immediately to a condenser operation for improving the power-factor of the transmission system, electric power producing operation or pumping operation.
While the water-wheel is in spinning reserve, the inlet valve mounted on the water line for introducing water into the runner chamber or draining water therefrom is in a closed position, and a plurality of guide vanes provided on the outer periphery of the runner for its entire circumferential extent and disposed in face-to-face relation with the runner are fully closed, so as to ensure that compressed air is filled in the runner chamber. However, although the guide vanes are fully closed, water will pass into the runner chamber by leaking through the gaps between the guide vanes, with the leakage increasing due to wear of the component parts and other factors as the result of prolonged operation of the water-wheel.
The invasion of the runner chamber by the leak means that the water in the casing between the inlet valve and the guide vanes and in the water line is replaced by the air in the runner chamber. The presence of air in the casing and water line causes a trouble when the water-wheel is switched from spinning reserve to a normal operation condition. To obviate this disadvantage, means is provided for providing an additional supply of water to compensate for the leak. Such means generally comprises a water conduit connecting a portion of the water line disposed above the inlet valve and nearer to the dam to portions of the water line and the casing nearer to the runner than the inlet valve by bypassing the inlet valve, and a valve generally referred to as a throttling and water supplementing valve which is mounted in the water conduit to reduce pressure.
In recent years, water-wheels have shown a tendency to have a high head and a great capacity. As a result, the pressure in the water line rises. This cause the leakage through the guide vanes into the runner chamber to increase.
If the volume of water leaking through the guide vanes into the runner chamber is great, the resistance offered to the rotation of the runner will be increased. This means that it is necessary to increase the capacity of the motor for driving the runner. To obviate this disadvantage, leak drain pipes for discharging the water passing into the runner chamber through leaks are mounted on the lower cover of the runner chamber and open at one end therein and at the other end in the draft tube, for example.
In the case of a pump water-wheel, the runner has a very high peripheral velocity in addition to an increased leakage of water due to an increase in the head. This increases the pressure applied to the outer periphery of the runner, and causes the water in the periphery of the runner to move with the runner, with a result that a vortex flow of high magnitude is produced and makes it difficult for the water to find its way between the outer periphery of the runner and the guide vanes. Thus, the water under pressure remains between the outer periphery of the runner and the guide vanes.
The fact that the area of opening of each of the aforementioned leak drain pipes cannot be increased is an important factor in this phenomenon. If the area of opening of each leak drain pipe could be increased, it would be possible to drain the water leaking through the guide vanes into the runner chamber to an extent such that no great difficulty is experienced in placing the water-wheel in spinning reserve. However, since the pipes open on the surface of the water flow passageway, it is impossible to increase the area of opening of each drain pipe without any restriction by disregarding the fact that the increase adversely affects the normal operation of the water-wheel for producing electric power or functioning as a pump. There are also limits to the number of openings.
To sum up, the increase in the head and size of water-wheels which has been realized in recent years is such that it is impossible to satisfactorily drain the water leaking through the guide vanes by increasing the area of openings of the leak drain pipes without interfering with the normal operation of the water-wheels to produce electric power or function as pumps. The water leaking through the guide vanes offers great resistance to the rotating runner. This will make it necessary to increase the size of the electric motor for driving the runner or cause disturbances in the current of the system.
In ordinary pump water-wheels, the compressed air supplied to the runner chamber is vented therefrom between the outer periphery of the runner and the guide vanes. However, since there is water under pressure in the outer periphery of the runner as aforementioned, the prior art has the disadvantages of not being able to drain the leak satisfactorily and of the temperature rising in the runner chamber.
The drawbacks of the prior art mentioned above can of course be somewhat obviated by reducing the volume of water leaking through the guide vanes by increasing the degree of precision with which the guide vanes are worked on and assembled. However, a prolonged use of the guide vanes inevitably results in an increase in the volume of water leaking therethrough.
It is known from our experience that the water-wheels which need attention in this respect are those which have a head of over 500 meters and that the runner of each water-wheel has a peripheral velocity of over 100 m/sec. In fact, there is no problem of draining of leak in pump water-wheels which have a head and a peripheral velocity below the aforementioned level, and draining of leak has been satisfactorily carried out through the leak drain pipes whose openings are increased to the allowable limits.